1. Field of the Invention
The present invention relates to a network of transceivers which monitor a defined geographic area for emergency transmissions, and which relay an alarm signal to a central station for appropriate action. More specifically, the invention is directed to an improved transmitter and transceiver network including a test mode for determining the operability of the electrical and mechanical components of the system.
2. Description of the Prior Art
Emergency transmitter systems are known in the art. Shields U.S. Pat. No. 4,998,095, issued Mar. 5, 1991, describes such a system for individuals within a predetermined geographic area like a campus, shopping mall, or stadium. A plurality of fixed transceivers at selected locations in the area monitor radio frequency emergency transmissions from portable transmitters. Transmissions include a code identifying the individual assigned the portable transmitter. The transceiver forwards this code, along with its own unique code, to a central station where the identity of the individual and his or her location is displayed. The location is determined from the unique code of the fixed transceiver that forwarded the information.
The success of the system depends, of course, on the operability of the transmitter, which may be adversely affected by a low battery, physical abuse, or the effects of the environment (such as, for example, exposure to humidity or dirt). Therefore, it is important that a user be able to test the transmitter from time to time. It is equally important that the test be one which will insure that the user is within the monitored region of a transceiver and that the emergency signal is actually being received by a transceiver. Other than by actually initiating an alarm, there is no provision in Shields for testing the system to determine operability.
Some known security systems do provide a test mode. Reich et al. U.S. Pat. No. 4,908,602, issued Mar. 13, 1990, relates to an emergency response system capable of testing the condition of a battery in a portable unit by physically setting the receiver for a test. The receiver then assumes that any transmission from the portable unit is for test purposes only, and no alarm signal is sent to the central monitoring station. While such an arrangement may be satisfactory for the Reich et al. system, where the user has physical access to the receiver, it is not particularly attractive for users of portable transmitters associated with inaccessible transceivers. The Shields transceivers, for example, preferrably are located where access is difficult. Similarly, when the system is intended for multiple users, there should be little or no risk it accidently will be left in the test mode or made unavailable during testing even for short periods of time.